Granholm and Lt. Gov. John Cherry both endorsed New York Senator Hillary Clinton last October. They're among seven Michigan Democratic superdelegates who backed Clinton.

Fifteen support Obama, with one more expected to endorse Friday.

Granholm spokeswoman Liz Boyd said Thursday that, while the governor has made it clear she'll support the Democratic nominee, she won't make a formal statement supporting Obama until after Clinton announces a decision on her campaign.

Clinton plans to hold an event in Washington Saturday to thank supporters and urge them to back Obama's candidacy.